os::tmpdir for Android

[sanxiyn]

Currently os::tmpdir returns /tmp on Android, but /tmp does not exist on Android. Android apparently does not have a global temporary directory so it is unclear what should os::tmpdir return.

[yichoi]

I suggest to use /data/tmp instead of /tmp. /data/tmp is not convention however most of developers use it instead of /tmp.

[flaper87]

Fixed by d1f9055 For android os::tmpdir now returns /data/tmp